I use slurry on synthetics too, especially when I am setting a bevel. I even go with slurry on a 600 grit sometimes when I have to work a big chip on a wedge or pre bevel set a wedge. I personally do not dilute, just go with it then wash off and go with no slurry to smooth the bevel a bit. I also found that slurry above 4k does not really do much , except on my Jnat finisher. May be I am wrong on this one I don't know.